How to Build a Solar Energy Generator for Emergency Backup Power

(Originally posted a few years ago. I’m reposting because of interest generated when I mentioned it in an article written earlier this week.)

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Over the last few months I’ve been reading various accounts of how people have been making their own solar generators and I knew that I had to give it a try. Think about it! Spend a few hundred bucks and you basically have a power source sitting in the house ready to go at any time that never needs gasoline, kerosene, or any other fuel except the sun. How cool is that? Why would I want a solar power generator? For a quick look at peak oil and what the government is doing about it check this out.

Parts

You will need a solar panel, charge controller, deep cycle battery and an inverter plus assorted wire and wire connectors. You can either leave it sitting on a bench or put it in some kind of housing system, which I’ll cover later.

Solar Panel The solar panel sits in the sunshine and delivers electricity to your system. How much juice gets delivered depends on the panel. This is a smaller system so I decided to try and get away with a small 20 watt panel. The good thing about these is that you can usually hook them up together to deliver more electricity.

This device sits between the battery and the solar panel and regulates how much charge the battery gets. It monitors the battery and will stop charging once it’s full, so that it doesn’t get damaged. Here’s the description right off the web site:

Charge controller prevents overcharging of 12-volt batteries

Intended for use with 12-volt solar panels

Handles up to 7 amps of array current and up to 100 watts of solar power

Charging light indicates the battery is charging, and a green light indicates a fully charged battery

Measures 4 x 1 x 2.5 inches (WxHxD) and weighs one pound

Price for the charge controller: $19.89

Inverter This is what actually delivers 120 volt power to your devices. It takes the 12 volts of electricity from your battery and converts it to 120 volts through some modern magic. The one I bought can also be hooked up to a car or truck.

Battery The deep cycle battery is what holds the electricity for the system. If you have large electricity demands you’ll need more than one battery in your battery bank. I bought a deep cycle marine battery from Walmart for around $100.

I figure that three batteries hooked together in parallel will be enough to meet my needs in case of a 24 hour power outage.

Next – Putting It All Together The first thing I did was hook the inverter up to the battery to see how well it worked. Beautifully, as it turns out. I ran a drill off it as a test and currently I’m running my laptop, external speakers, and a lamp and after two hours of use haven’t noticed much drop in the battery’s voltage. It started out at 12.3 volts and is currently sitting at 12.1 V. Needless to say if you’re in a black out situation you could run several small items like these. One of the cool things about the inverter is that it has a USB port so you can charge your MP3 players or whatever directly from the device while it’s turned on. Pretty sweet!

Once the inverter was connected to the battery I hooked up the charge controller like this:

Next I hooked the solar panel to the charge controller and set the panel outside to start charging.

The wire from the solar panel to the charge controller can be seen being held in place by a pellet bag just above the laptop.

Small Solar Panel

How big an inverter do you need? The first thing to do is figure out how much power you’ll need if the power goes out. I want to be able to run a pellet stove or a freezer, so let’s use the freezer as an example. *Warning* Geeky stuff follows.

You can usually find the electrical information on the back of the appliance, but if you don’t see it a trusty Google search can usually help you get the information you need. My freezer uses 115 volts and 5 amps for a total of 575 watts. (volts x amps = watts) I have a 1500 watt inverter, so even factoring in the startup voltage (motors have a higher energy draw when they first start up) I still have enough power in the inverter to comfortably run this device.

I could also run the laptop and a few other small gizmos, but if you tax the inverter too heavily it needs to shut down and allow time to cool off every once and awhile. Still, the freezer doesn’t run continuously, so it should be fine.

The Battery Bank Granted, one battery isn’t much of a bank, but I’ve pretty much determined at this point that the system isn’t going to get a lot of heavy use. I figure that one 120 amp hour deep cycle battery could run the freezer continuously for roughly three hours before it dies.

Testing In the last few days the laptop and speakers have run off the system without any problem at all. I haven’t yet tested the voltage being produced at noon, but I have noticed that the battery is being charged up 12.5 volts during the day thanks to some sunny skies. So far the system has been a success and my girlfriend thinks it’s pretty cool too.

Other Stuff There are a lot of things I haven’t touched on here due to the amount of information I had to dig through. For example: batteries create hydrogen when they’re charging and need to be properly ventilated. Battery maintenance in and of itself is a huge part of a solar array.

Cabling is another factor. I’m using #14 wire used to run electricity to outdoor lighting and it should really be #12 or #10 wire, but for what I’m using it for it should work fine. When I add to the system I will have to upgrade the wiring.

Size of the system. In order to figure out how many solar panels and batteries you need and the rating on the charge controller and the inverter you need to start with what you want to run and then give it a healthy boost because we don’t have sunshine every day.

Further Plans One more thing I want to do with this system is put it in a container. I happen to have a wheeled tool box sitting around not being used and I’m planning on putting it in that. The bottom half of the toolbox will house the battery and the top will hold the inverter.

Containment System (an old toolbox)

There are two reasons for doing this. One is to keep it out of the way of my young son who is intensely curious about Dad’s projects and the second is because that sucker is heavy! If I’m going to wheel this thing say, out to the truck from my basement, it’s nice to have it all in one unit that I can pull along behind instead of trying to carry it.

One important note for anybody who might try to build one of these: If you do put your battery in a system like this make sure it’s vented! I’m going to put a small fan on the battery container that will vent the hydrogen out as the battery charges.

Eventually I want to add enough panels and batteries to this system to run a pellet stove off it full time. So, I’m not quite ready for the zombie apocalypse quite yet, but like the rest of you preppers I’m working on it!

If there are any experts out there with ideas for this project please let me know!

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